First, why generate several keys? The main reason is privacy. Since you can see the balance of all addresses, it is better to use a new address for each transaction.
You can generate a key, like you did at the beginning:
var privateKey = new Key()
However, you have two problems with that:
All backups of your wallet that you, have will become outdated when you generate a new key.
You cannot delegate the address creation process to an untrusted peer.
If you are developing a web wallet and generate keys on behalf of your users, and one user gets hacked, they will immediately start suspecting you.